1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to a developing unit removably mounted to an image forming apparatus, and an image forming apparatus having the same.
2. Description of the Related Art
Generally, an image forming apparatus includes a paper feed unit, a developing unit, a transfer unit, a fusing unit, and a paper discharge unit.
Most of the developing units employed in image forming apparatuses for home use are formed as a single body with the developer cartridges, while most of the developing units for office use are separately provided. Because the image forming apparatuses for office use are required to output far more printouts than printouts for home use, maintenance will cost a lot if the image forming apparatuses for office use employ the developing cartridges and the developing units as a set.
While the developer cartridge is replaced frequently, the developing unit, housing therein a photoconductive medium and developing member, is used for a longer period of time. Thus, replacement of the housing unit is less frequent and occurs when the photoconductive medium is too old to react to light exposure, or when image quality degrades severely.
The developing unit is mainly categorized into contact and non-contact types according to the type of developer the developing unit employs therein. FIG. 1 illustrates an example of a non-contact type developing unit.
A photoconductive medium 10 is rotatably disposed on a first frame 1, and a developing roller 20 is disposed on a second frame 1a to feed the developer to the photoconductive medium 10. The second frame 1a is capable of pivoting about the first frame 1.
The developing roller 20 necessarily keeps a predetermined developing distance from the photoconductive medium 10 so that an image can be formed with proper density. Accordingly, developing gap maintaining discs 30 are disposed on both ends of a developing roller shaft 21. The developing roller shaft 21 rotatably supports the developing roller 20.
The developing gap maintaining discs 30 are rotatable in association with the rotation of the developing roller 20 and the developing roller shaft 21. The developing gap maintaining discs 30 are made by plastic molding, and are disposed to rotate in contact with the non-image area.
However, problems occur when the photoconductive medium 10 is maintained in contact with the developing gap maintaining discs 30. First, an unexpected impact may be exerted to the developing unit when the developing unit is moved or operated, subsequently causing physical damage to the developing gap maintaining discs 30. Subsequently, the damaged developing gap maintaining discs 30 do not maintain the desired developing gaps, and as a result, image quality degradations such as creasing occur. In order to avoid this problem, keeping the photoconductive medium 10 and the developing gap maintaining discs 30 at distance when the developing unit is not mounted to the image forming apparatus is necessary.
FIG. 2 illustrates an example in which the second frame 1a is temporarily fixed in place to keep the photoconductive medium 10 at a distance from the developing gap maintaining discs 30 to prevent unwanted damages to the developing gap maintaining discs 30.
Most of the rotating components such as the developing roller 20 and feeding roller 25 are fixed to the second frame 1a housed in the developing unit, and the second frame 1a is hinged to the first frame 1 to turnably move between a first position and a second position. The second frame 1a is in a first position when the developing unit is mounted to the image forming apparatus and the photoconductive medium 10 contacts the developing gap maintaining discs 30, and moved to a second position when the developing unit is demounted from the image forming apparatus and the photoconductive medium 10 is separated apart from the developing gap maintaining discs 30.
Accordingly, a separate fixing member is required to fix the second frame 1a in the second position. Generally, a rubber pin 1b is passed through the developing unit from outside to prevent rotation of the second frame 1a. 
However, most of the printer users are not familiar with detailed structure of the components. When a unknowledgeable user tries to replace the developing unit, the user likely puts the developing unit in the image forming apparatus without knowing that the rubber pin 1b should be removed beforehand. In this case, because the developing gap maintaining discs 30 do not contact the photoconductive medium 10, the proper developing gap is not maintained during the operation of the image forming apparatus and image error occurs.
Furthermore, a requirement for the removal of the rubber pin 1b before mounting the developing unit is inconvenient for the user.